Phase splitter



Dec. 8, 1959 w. e. REICHERT, JR 2,916,663

PHASE SPLITTER Filed June 14, 1957 INVENTOR.

WILLIAM 6. RE ICHERT, JR.

BQJJ Q 09% A TTORN E Y5 2,916,663 PHASE SPLlTTER William G. Reichert, Jr., Cedar Grove, N.J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N.J., a corporation of Delaware Application June 14, 1957, Serial No. 665,782

20 Claims. (Cl. 31519) This invention relates to phase splitters, and more particularly to apparatus which produces both a pos1t1ve atent' going and a negative going output signal in response to a single input signal.

Two types of signals are widely used in electronic circuitry, the first being known as single ended, wherein the signal is either positive going or negative going; and the other type being designated as balanced, which provides both a positive going and a negative going signal. Frequently, a particular circuit will require balanced input signals whereas the preceding circuit produces only single ended output signals. In cases such as these a phase splitter is required, this apparatus being energized by a single ended signal and producing a balanced output; i.e., both a positive and a negative going signal. 6

Prior art phase splitters had many shortcomings since they invariably utilized active elements such as electron tubes. These required power to operate them, a good deal of associated circuitry, and invariably introduced frequency limitations. In addition, the output circuits of prior art phase splitters generally produced signals which appeared to come from sources having difierent impedances.

It is therefore the principal object of my invention to provide an improved phase splitter.

It is another object of my invention to provide a phase splitter which does not require active elements.

It is a further object of my invention to provide a phase splitter which provides output signals which appear to come from sources having the same impedances.

It is a still further object of my invention to provide a phase splitter which has a better frequency response than heretofore possible.

"The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawing in which;

Fig. 1 illustrates a basic form of my invention.

Basically, my invention contemplates the use of a delay line formed into a configuration which resembles a Y. The inputsignal is fed into the bottom of the stem, and branches-off into the two arms. the delay line configuration so that one arm terminates in a short while the other arm terminates in an open, it being well known that out-of-phase signals will be reflected from the ends of these arms. These reflected of 22; and arm portions 22 and 24, each also having a characteristic impedance of 2Z. Arm portion 22 terminates in an open configuration wherein the central wire is insulated from the outer sheath, while arm portion 24- terminates in a shorted configuration wherein the inner wire is conductivelyconnected to the outer sheath. There are many forms of delay lines, e.g., the lumped constant type, and the twin lead type, etc., but while any delay line may be used, coaxial cable has a number of advantages, namely, connections to it are easily made, generally by use of T connectors; it is immune to external disturbances, such as handling or pickup of stray signals; it is well shielded and relatively immune to signals in other parts of the cable, and may therefore be coiled to save space; and finally coaxial cable-is readily available in a widechoice of types, permitting the use of suitable lengths, diameters, and propagation velocitiesand impedances.

Basically, my invention operates as follows. An input signal 26, shown as a positive going signal which it is desired to display on the faceplate of tube 10 is applied to input terminal 28. The input signal is shown for convenience as a pulse, but it may have any shape depending upon its information content. It traverses stem portion 16 and at time t reaches fork A, where the signal lines are connected together, whereupon the signal traverses branch portions 18 and 20. It will be recalled that stem portion 16 has a'characteristic impedance of Z, whereas branch portions 18- and 20 each have a characteristic impedance-of 2Z. It will be seen that at fork A, branch portions 18 and 20 are in parallel, and therefore their composite impedance is /2 of 2Z or Z which matches the impedance of stem portion 16. Since there is no change of impedance, no reflections occur at point A, and the incoming signal splits into two voltage signals, each substantially equivalent in amplitude and phase to input signal 26. Each of these traverse one of the branch portions to points B and C,

such equal amplitude similarly phased signals is known I as a common mode signal. A

Each arm portion .22 and 24 has a characteristic impedance of 22, and therefore exactly matches'the impedance of its feedingbranch portion 18 or 20 which I arrange anti-phase signals are applied to a utilization device such as the deflection plates of a cathode ray tube, which therefore obtains the balanced signals for which it is designed.

The physical aspect of my invention is shown in Fig.

1 1 which illustrates, as a utilization device, a standard of, reaching them at time 1 also have an impedance of 2Z. Thus, there are no reflections at points B or C. The signals therefore enter I I thevarm portions, and are propagated to the ends there- I The signal traversing arm 22 is reflected from the open end thereof in exactly the same phase, the reflected in-phase signal traveling back toward point B, and reaching it at itime t, after an interval determined by its velocity of propagation and the length of the arm portion 22 of the delay line. Meanwhile, the positive going signal at point C is propagated along arm 24 toward the end thereof. Since'this end is terminated in a shortvcircuit, the positive going waveform experiences a phase reversal, i.e., it is reflected as a negative going signal which travels back toward point C, and reaches it at time t, after an interval which depends on the length of arm portion 241and 22 and 24 are identical, exceptfor the type of terminabalanced deflection signal which causes the electron beam to be deflected.

Ideally, the connections from deflection plates 12 and 14 should be of smaller capacitance than the delay lines, or should be otherwise matched so they do not introduce any discontinuity or mismatch.

Each signal continues to be propagated toward point A, and since in this direction there is a mismatch, reflections now occur at this point. These reflections reverberate in the delay line until they are dissipated by losses therein, whereupon the apparatus is ready for another input signal.

My inventionias described, provides a voltage gain of 2, since for a given amplitude of input signal the same amplitude and phase is applied to one deflection plate, whilethe same amplitude of opposite phase is applied to the other deflection plate. If there is a mismatch at fork A for the incoming signal, the gain will be decreased or increased depending on thetype of mismatch. For example, if the incoming signal at point A encounters a higher impedance, the voltage signal will be increased.

Stem portion 16 may of course be of any convenient length, or in the extreme case, may be non-existent, in which case the delay line configuration takes the form of a V with the input signal applied to the point thereof. The propagation velocity of stem portion 16 is not critical, the primary requirement being that it form the desired impedance with the branch portions 18 and 26. The branch portions form the desiredimpedance match at point A, and each must be identical with the other branch. Similarly, the arm portions must be identical, and form the desired impedance match with the branch portions. The length of the arm portions is preferably such that the common mode signal has disappeared before the reflected signal is applied to the utilization circuit. Similarly, the length of the branch portions shouldbe such as to permit the reflected signals to be completely applied before reflections from fork A appear. After this time the tube is blanked out so that nothing appears on the faceplate.

These relationships may be stated as follows. Let L be the length of a delay line portion which is identifiedby a subscript a or b for arm or branch. Similarly, let V represent the propagation velocity, u or b again indicating -the portion under consideration. The letter W may then be used to designate the signal width or duration. Referring again to Fig. 1, it will be realized that the leading edge of the common mode signal appears at point B (or C) at time t and reaches the end of the delay line at time 1 thus requiring an interval of t t =L+V microseconds. Since anequal interval is required for the reflected leading edge to traverse the same path, the elapsed timeis 2L -:Vg,. In order to prevent overlapping ofJ-the incident and reflected signal, the leading edge of the reflected signal should arrive at point B (or C) after the trailing edge of the incident signal has passed. Thus, the length of the arm portion should be long enough sothat the transit time in the delay line is greater than the pulse width or duration, i.e., (2L -:V) W or L,, (WV,,-:2). i

A similar situation exists with respect to the balanced signals and the reflectionsfrom fork A. Similar reasoningwill indicate that in order to prevent the overlapping of signals, the. length of the branch portion may be expressed L (WV -:-2). If there is a mismatch at points B. or C, another situation arisw. In this case, spurious reflections are produced when the leading edge of the input signal first reaches B and/or C. These reflections travel back to fork A, and are again reflected hack to points B and/ or C. The length of the branch portions should be such that these reflections at points B and/ or C do not interfere with the useful pulse.

The foregoing discussion has beengiven in terms of the information signal usually applied to the vertical deflection plates. It is of course possible to apply signals to the other, or horizontal, set of deflection plates, one illustration being the use of a sawtooth waveform to produce scan, for the moving of the electron beam across the face of the tube.

ffhile I have disclosed the principles and one embodiment of my invention, others will occur to those in related arts. I desire therefore to be limited not by the foregoing illustrations and explanations, but rather by the following claims.

What is claimed is:

l. A phase splitter comprising: a pair of equi-length delay lines connected in the form of a V, each said delay line of said configuration having series-connected branch portions and arm portions, one of said arm portions terminating in a short circuit and being isolated from any other circuitry, the other of said arm portions terminating in anopen circuit and being isolated from any other circuitry; and a utilization device having one input terminal thereof connected to one of said delay lines at the junction. of its said branch and arm portions thereof, and having another output terminal thereof connected to the other said delay line at the junctionof its said branch and arm portions whereby the ends of the arm portion-reflect out-of-phase signals which are applied to respective terminals of said device.

2.The device of claim 1 including means to apply an input signal. to. the point of said V whereby said input signal is reflected from the ends of said arm portions in theform of anti-phase signals which are applied to said utilization device.

3. The device of claim 2 wherein the length of said 1 arm portion is greater than one-half the product of the signal width multiplied by the said arm portion.

4. The device of claim 2 wherein the length of said branch portion is greater than one-half the signal width multiplied by the propagation velocity in said branch portion.

5. The device of claim 2 wherein the length of said arm portion is greater than one-half the product of the signal width and the propagation velocity in said arm; and the length of said branch portion is greater than one-half the product of said signal width and the propagation velocity in said branch portion.

6. A phase splitter comprising: a pair of equi-length delay line configuration in the form of a Y, said configuration having a stem portion and a pair of delay lines having their signal lines electrically connected directly to the signal line of said stem portion, one of said pair of delay lines terminating in an open circuit that is isolated from any external circuitry, and the other terminating in a short circuit that is also isolated from any external circuitry, whereby an input signal applied to the bottom of said stem portion would be re flected in the same phase from said open termination, and in the opposite phase from said shorted termination; a first output circuit connected to an intermediate point of one of said pair of delay lines; and a second output circuit connected to a similar point on the other of said pair of delay lines, whereby one of said output circuits will receive an in-phase reflected signal, and said other output circuit will receive an out-of-phase reflected signal, thus producing balanced signals for a utilization device.

7. The device of claim 6 wherein each said pair of delay lines has a characteristic impedance which is twice that of said stem portion.

8. The .device of claim 6 wherein said output circuit connections are further from said terminations than onepropagation velocity in half the width of the input signal multiplied by the propagation velocity in said terminated delay lines.

9. The device of claim 6 wherein said output connections are further from said connection with said stem portion than one-half the width of the input signal multiplied by the propagation velocity in said terminated delay lines.

10..The device of claim 6 wherein said output circuit connections are further from said terminations than onehalf the 'width of the input signal multiplied by the propagation velocity in said terminated delay lines; and said output connections are further from said connection with said stern portion than one-half the width of the input signal multiplied by the propagation velocity in said terminated delay lines.

11. The device of claim 6 including means to apply an input signal to the bottom of said stem portion.

12. A phase splitter comprising: a delay line configuration in the form'of a Y, said configuration having a stern portion, branch portions, and arm portions, one of said arm portions terminating in a short circuit and the other of said arm portions terminating in an open circuit; and a utilization device in the form of a cathode ray tube having one deflection plate connected to the junction of one of said branch and arm portions, and having the other deflection plate connected to the junction of the other of said branch and arm portions.

13. The device of claim 12 wherein the characteristic impedance of said branch portions is twice the characteristic impedance of said stem portion.

14. The device of claim 12 wherein the characteristic impedance of said arm portions equals the characteristic impedance of said branch portions.

15. The device of claim 12 wherein the characteristic impedance of said branch portions is twice the characteristic impedance of said stem portion; and the characteristic impedance of said arm portions is equal to the characteristic impedance of said branch portions.

16. The device of claim 12 including means to apply an input signal to the end of said Y.

17. The device of claim 12 wherein the length of said arm portion is greater than one-half the product of the signal width multiplied by the propagation velocity in said arm portion.

18. The device of claim 12 wherein the length of said branch portion is greater than one-half the signal width multiplied by the propagation velocity in said branch portion.

19. The device of claim 12 wherein the length of said arm portion is greater than one-half the product of the signal width and the propagation velocity in said arm portion; and the length of said branch portion is greater than one-half the product of said signal width and the propagation velocity in said branch portion.

20. A phase splitter comprising: a delay line configuration in the form of a Y, said configuration having a stem portion, two identical branch portions, and two identical arm portions, one of said arm portions terminating in a short circuit and the other of said arm portions terminating in an open circuit, the length of said arm portions being identical and greater than one-half the product of the signal width and the propagation velocity in said arm portion, the length of said branch portions being identical and greater than one-half the product of said signal width and the propagation velocity in said branch portion, the characteristic impedance of said branch portions and said arm portions being equal and being twice the characteristic impedance of said stern portion; a utilization device in the form of a cathode ray tube having one deflection plate connected to the junction of one of said branch and arm portions, and having the other deflection plate connected to the junction of the other of said branch and arm portions; and means to apply an input signal to the end of said Y.

Caraway May 19, 1953 Hyman Jan, 5, 1954 

